In that poll, Gallup found 58% of Americans support legalizing marijuana. The increase in support for legalizing comes from Independents. Sixty-two percent of Independents now favor legalization. That is a 12% increase during the last year.

When Gallup first asked about legalization in 1969, only 12% favored legalizing marijuana. Support for legalization doubled in the 1970s, plateaued during the 1980s and 1990s, and slowly moved higher since 2000 -- reaching 50% in 2011.

Colorado and Washington recently became the first states to legalize recreational use of marijuana. The new polling suggests they won't be the last.